318 into a 340

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littleman66

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i found a 318 with the 2.02 heads on it, it came out of a school bus. asking 200 Can for complete engine.

my dad says them 318 are the same stroke as the 340, therefore you can bore it out to be a 340. i havent heard of this? what do you guys think?

either way im buying the engine for the heads....
 
i found a bit of information, and you can bore them out but you will have heating problems, but there is a poly 318 engine that is much wider, how would i determine if the engine is a poly 318?

the man that ouns the engine said the 318 had a name for it that he forgot, im guessing it might be the poly?
 
can't tell you on the poly. i do know that the 318 poly engines were in the 61-65 range i think?. just keep the 318 with the 2.02 heads , do a small overbore for compression 9.50 to 1 (89 octane pump gas) or so and maybe stroke it out alittle. that engine is able to crank out some good power with not alot of work.
 
i found this it may help. i also saw a few drawbacks on the poly engines. mainly part availibity or lack there of. check into it carefully before you jump into it. maybe someone else can advise you on this.

The 277-318 old style cylinder head is generally called a poly-sphere. Looking at the strange valve angle it appears to be a modified Hemi. It certainly isn't a wedge. The casting number is 2268341.
 
so will these "poly" heads flow better then a set of J heads because of the hemi like design

like i said before, is it possible to bore the poly block into a 340? or will i run into overheating problems
 
No you can not bore a 318 to 340 bore size. You may be able to go to 4.000 inch (360 bore size) if the block sonic checks out OK. If the heads have a shaft rocker set up or simply a standard valve cover, then there not poly heads.
If the valve cover has waves or wavy bottom, then it's a poly head. There a canted valve design. The head can be ported to a decent level. It will not port out better than a LA head. The design of the head in other makes is more advanced than the older Poly head and much more potential.
Chevy heads are of this design. There revised ports would have been much more inline with that heads evolution should Chrysler had decided to continue with that head.

The Poly head was also nicked named "Semi Hemi" head. Performance parts for the older poly engines are out there. Headers are very expensive, intakes are used save the Weiand low rise single plane which is made new. Cams can be made new. Racer Brown has a grind list of over 100 cams ready to grind or custom cut for you.

The MoPar engines book has a list of parts the "A" and the :LA: share.
 
318 block will only bore to 4.00'' if you sonic check it. And 318 poly heads have a square valve cover with two studs in center of valve cover to hold it on.
 
littleman66 said:
i found a bit of information, and you can bore them out but you will have heating problems, but there is a poly 318 engine that is much wider, how would i determine if the engine is a poly 318?

the man that ouns the engine said the 318 had a name for it that he forgot, im guessing it might be the poly?
Click to expand...
You can't bore a 318 to a 340. You should never bore any Mopar more than .020 or.030. You can loose the integraty of the bore. The bore may not stay perfectly round and the rings may not seal good, because the cylinder walls will be too thin. Not to mention other problems. Also, a poly 318 has scalluped shaped valve covers with 2 bolts in the middle. Don't even think about swapping parts between the two. What makes you think that 318 has 2.02 heads? Highly unlikely comming out of what it was in. THUNDERBUMPER
 
From Allpar:

"The A block was fractionally bigger in external dimensions than the LA block, although it was heavier due to the new casting techniques. The LA block 273 weighed 55 pounds less than the poly 318, both used 4.46" bore centres, and both were 21.4" in length, without water pump, crankshaft, etc. The poly heads are much wider and heavier than the LA's wedge heads and that gives the A block engines the appearance of being bigger than the LA engines."

Here's more:

http://www.allpar.com/mopar/poly.html

Is this why you think it has 2.02 heads?
 
I don't think any production 318 ever produced had 2.02 heads stock. The biggest intake valves produced were on the Magnums with 1.92? If I remember correctly.
 
Your right Black Ace. 1.88's in the 4bbl option.
 
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